In radiological practice, radiographic images are used for a variety of diagnostic purposes. Radiographs can be captured to detect and identify lesions, to diagnose an underlying pathology from radiological manifestations, to assess the existence and extent of a fracture etc.
There exist also a domain of specialized radiological examination procedures, which cannot be classified into any of the enumerated tasks, which is the field of radiological scoring.
In radiographic scoring methods,the radiographer or clinician already knows the pathology but wishes to assess the degree of severity of the disease or the developmental stage of the patient.
Several scoring methods exist in the state of the art. All scoring methods have the following specific characteristics in common:                (1) a number of pre-determined anatomical sites on a radiograph is examined; the number of anatomical sites being constant for a given method;        (2) the specific appearance of the anatomical site is rated against a number of reference pictures, each reference picture corresponding to a developmental or pathological stage, and the rating results in a stage being assigned; the number of reference stages being constant for the given anatomical site;        (3) each stage has an associated numerical score, the value of which in general differs according to the stage and the skeletal site;        (4) all scores are totaled and translated into a clinically useful index.        
Although rating refers to the process of assigning a stage to an anatomical site and scoring refers to the attribution of a value to the stage, we will call both processes ‘scoring’ in the sequel.
Radiological scoring methods, which adhere to the aforementioned principles, are e.g. bone age determination (also known as skeletal maturity assessment), rheumatoid arthritis scoring, osteo-arthritis scoring, ankylosing spondylitis scoring, and osteoporosis assessment.
In the following scoring methods applied to different applications will be explained.
A first example of an application wherein radiographic scoring is used, is skeletal maturity assessment, a procedure frequently performed in paediatric radiology.
Biologically, it is desirable to assess the maturity of the whole skeleton, but because of several practical difficulties such as the time needed for the assessment of so many bones, the expense of radiographic film, the risk of excessive radiation exposure etc. a specific area is chosen for the assessment of skeletal maturity.
An area of the human skeleton, which has received considerable attention as a source of clinically relevant maturity indicator, is the hand-wrist. Based on a radiological examination of skeletal development of areas of the non-dominant hand and wrist, the bone age is assessed and compared to the chronological age. A discrepancy between these two values indicates abnormalities in skeletal development. This examination is performed on children with growth abnormalities to affirm clinical suspect, to predict height at adult age, or to monitor the effect of treatment of metabolic diseases.
A common method for assessing the skeletal maturity is the atlas method, and the hand-wrist was the first area of the body for which atlases became available. Currently, there are two frequently used atlas methods operating on a hand-wrist radiograph.
The most frequently used method (78%) is the Greulich and Pyle (GP) method. In this method, the radiograph of non-dominant hand wrist (mostly the left hand) is compared to a reference series of hand-wrist radiographs displayed in this atlas. Each hand-wrist radiograph corresponds to a certain year of bone age. The age interval between successive hand-wrist plates varies from 3 to 6 months. The reference radiograph, which globally compares best with the clinical image, is selected as the best match and its associated age is called the bone age. This atlas-derived bone age is then compared with the chronological age of the patient, and the age difference is used for diagnostic purposes.
The manual effectuation of this method is prone to error or susceptible to ambiguity.
Firstly, different radiologist performing this procedure may have different training experience; hence substantial inter-observer and intra-observer variance may result from the subjective nature of this comparison.
Second, the comparison is a global one. Depending on the weight the radiologist attaches to the similarity or dissimilarity of specific skeletal sites on the hand-wrist radiograph, ambiguous results may be obtained.
A method, which aims at minimizing the subjective observer errors, is the Tanner and White house method (TW2 method). Scores are assigned to grades of skeletal maturity indicators, and the sum of scores is later transformed to a skeletal age (also called bone age). Slight modifications to the reference values and charts have recently been made to reflect changes in the population, resulting in the TW3 method. Descriptions and manual rating of the stages of the bones, however, have not been altered.
The TW2 method is currently effectuated in paediatric radiology as follows.
A radiograph from the non-dominant hand and wrist is made either by (a) conventional screen/film recording system, or (b) by digital means such as film digitisation, a computed radiography system or a direct radiography system (based on direct or indirect flat panel, or CCD).
In case a film is used, it is viewed on a light box. A digital image on the other hand may be either printed on film and viewed conventionally on a light box, or it may be displayed on a viewing station.
Knowledge of gender and chronological age of the patient are the only two clinical data needed to start the analysis.
For each skeletal site indicated in the atlas for which a score needs to be established, the corresponding skeletal site in the actual hand-wrist radiograph is searched for visually. Specific salient anatomic details of the skeletal site are retained mentally.
Then the attention is directed to the different stages depicted in the atlas to identify the most similar one.
Use is made of (1) the reference pictures (two radiographic reproductions per stage in the TW2 atlas, to reflect the range of variation within the stage), (2) a sketch or drawing of the skeletal site depicting the outline of the bones, the radio-opaque lines on or within the margin of the epiphyses and bones and pointers to salient features of the particular stage, and (3) one or more criterions per stage, which are textual explanations hinting at the most prominent image features of the stage.
In the event of doubt, whether a particular feature of a certain stage is present or not in the actual image, visual attention is redirected back to the hand-wrist image on the light box or computer display.
As a matter of course, the correct skeletal site to be assessed needs again be relocated in the hand-wrist radiograph before such confirming visual analysis can be effectuated.
In many cases, if not all, several switches back and forth between hand-wrist radiograph and the reference stages in the atlas are needed before a conclusive assignment of a reference stage can be made.
The score, corresponding to the matching stage, is written down on paper or typed in a computer spreadsheet or database.
This iterative process of hypothesis generation and hypothesis verification as to the actual stage of a skeletal site is repeated s for every skeletal site.
In the full TW2 method, 20 skeletal sites in the hand-wrist need to be assessed this way; therefore this scoring method can be time-consuming, demanding and error-prone.
The total score (on a scale between 0 . . . 1000) is translated into a bone age by a table look up operation. A different table is applied depending on the gender of the patient.
The bone age derived is compared with the chronological age of the patient and the difference between them is used as an element in the clinical diagnosis process.
Analogous to the Greulich and Pyle method, care must be exercised when interpreting the bone age to chronological age difference for patients belonging to a race other than the Caucasian type, because the atlas shows reference pictures and associated scores for this ethnic type only.
Unfortunately, although reliable, the above method is complex to operate for several reasons:                It requires a well-trained radiologist or radiology operator.        Because it requires the assessment of a great number of different skeletal sites, a manual method is time consuming.        The application of the method by means of analogue screen-film radiography is particularly cumbersome. It requires 3 distinct media to effectuate this procedure:                    An X-ray film of the hand or other skeletal sites, displayed on a light box. With the emergence of digital radiography modalities (film digitisation, computed radiography, digital radiography sensors), the digital image may be displayed on a computer display instead. However, such electronic medium still is physically distinct from the remaining components.            The TW2 atlas illustrating the different reference skeletal stages to compare with, and depicting the conversion table to manually convert the total score into a bone age.            Pencil/Paper to note and add the scores of each selected stage in the patient dossier. Alternatively, electronic spreadsheets may be used in conjunction with a database to store and compute the total score and the conversion to bone age. This way of operation is particularly cumbersome when scores determined at regular time intervals need to be retrieved and compared for clinical evaluation over time.                        Both TW2 and GP atlases have been established for the Caucasian racial type. Therefore, the bone age derived from these atlases is in principle valid for this type only.        
Another example of an application wherein radiographic scoring is used, is rheumatoid arthritis.
Conventional rheumatoid arthritis scoring (RA scoring) is based on comparison of the actual film radiography of hands and feet with reference pictures printed on film.
To establish the database of reference pictures, all stages of a joint or a group of joints are printed on one sheet of film in life size.
Scoring proceeds by displaying standard reference films and the actual radiography on a light box, and writing down scores associated with the matching stage of each joint.
Among other indicators, the most specific deformations in RA are erosions and joint space narrowing. The radiological study of these deformations is complementary; therefore, both are being assessed in a scoring method.
Radiological assessment serves as a recognized standard for the evaluation of rheumatoid arthritis. For standardized, epidemiological and therapeutic evaluation, scoring or grading systems have been proposed on X-ray images of specific skeletal sites. X-ray images have the advantages to be able to record the history of the damage of a joint, because the damage is mostly irreversible. Previous images can be recalled in a later stage, to assess the evolution and to subject them to newly developed scoring systems. The effectivity of drugs can be traced.
These advantages however, can only be obtained when the images are of sufficient diagnostic quality: (a) for serial assessment, the positioning of the joints during radiation exposure are of substantial importance, (b) correct exposure is important because overexposure or underexposure affects e.g. the correct assessment of erosions, and (c) the images recorded with sufficient resolution are essential for a reliable evaluation of previous erosions.
Still another example of an application wherein radiographic scoring is used, is osteoporosis scoring.
Spine or hip fracture due to minor or no trauma is an essential feature of symptomatic osteoporosis. Conventional radiographs are widely used to confirm or disprove suspected osteoporotic fractures, and may also demonstrate progress of existing fractures or development of new ones.
The scoring systems using conventional radiographs suffer the same drawback of other film-based diagnostic scoring systems. As indicated, the problem of repeated re-location of the anatomical site is even more compound because the spine is a highly repetitive structure of vertebrae having almost identical shape.